Now I just need to be able to save the value of this dropdown list when the comment is posted as a meta data of this particular comment. Note that this is a plugin and I dont want to modify core wordpress files as suggested in a tutorial here. I found a relevant discussions on the wordpress forum but I still could not find the answer I was looking for.

How can I save the selected option value as a comment meta in wordpress database?

Do I need to use AJAX for this or can this be achieved by simply using an action or filter that I could use to retrieve the value of the dropdown menu?

Thank you for your response. As I asked in the question I wanted to save the data as comment meta. Please edit your answer to save for comment meta instead of user and I will accept it.
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ArasJul 30 '12 at 23:48